Plug-in commutator and process for its manufacture

ABSTRACT

In the case of a plug-in commutator with a hub body (1) consisting of an electrical isolation material and having evenly distributed and positioned grooves of like design over its circumference, in which each of the segments (5)--of like design--which form the commutator path, is inserted by forming a form-fit connection in radial direction, the segments (5) are safeguarded from a shift in relation to the hub body (1) by a clamping force that is based on an overdimension (x, z) of the segments (5) and/or of material parts of the hub body (1) that facilitate the positioning of the segments (5). Only in the area of the two end sections (18, 21) of the segments (5) and/or the grooves is the overdimension (x, z), which determines the clamping force exerted on the segments (5), provided.

BACKGROUND OF THE INVENTION

The invention concerns a plug-in commutator, and a process for itsmanufacture.

In a known plug-in commutator of this type (WO 95/14319), the forceneeded to insert the segment into the groove is so great thatdisturbances during insertion cannot be ruled out. If one were to reducethis force by reducing either the overdimension of the segments and/orthe underdimension of the groove, then a reliable positioning of thesegments in the hub body can no longer be guaranteed.

OBJECTS AND SUMMARY OF THE INVENTION

The problem the invention seeks to solve, then, is to create a plug-incommutator in which the segments are positioned in a reliable fashion inthe grooves in spite of the fact that the force necessary for theinsertion of the segments into the grooves is reduced. The plug-incommutator solves this problem with the properties of the independentapparatus claim, whereby below an overdimension, an underdimension thatbrings about a clamping force is also understood. A process for themanufacture of the plug-in commutators according to the invention isalso the subject of claim 15 the independent process claim. Advantageousdesigns of the plug-in commutator according to the invention and themanufacturing process according to the invention are the subject matterof the subclaims.

For an exact and reliable positioning of the segments in the grooves, itis completely satisfactory--as has been demonstrated--when the maximumvalue of the clamping force exerted on the segments is determined by theclamping in the area of the two end sections of the segments. Moreover,the result of this is that the high clamping forces, and in turn, thefriction that must be overcome when inserting the segments in thegrooves, occurs only in the two end sections, which considerably reducesthe force necessary to insert all the segments in the grooves at thesame time, whereby the maximum value of this force only occurs when thelagging end of the segments enters into the grooves.

In a preferred working model, the grooves have the necessaryoverdimension in that end section that takes up the leading end of thesegments during insertion; and the segments have the necessaryoverdimension in the segments in their lagging end sections. Thesegments, then, can be inserted into the grooves with very little forceuntil the leading end reaches the end section of the grooves displayingthe overdimension and the leading end section of the segments enter intothe grooves.

The axial extension of the zones that have the overdimension can bedifferent. In this connection, a larger axial extension comes intoconsideration in both the area of the end section of the segments thatlead during insertion and in the area of its lagging end. In thepreferred model, the axial extension of the zones displaying theoverdimension is around 15% in the area of the leading end section; inthe area of the lagging end section it is around 5% of the length of theparts of the segments forming the commutator path.

In the middle section of the segments and grooves that lies between thetwo end sections a gap can exist between the surface areas of thesegments, which overlap in radial direction, and the hub body;relatively speaking, this gap is usually, however, quite small.

In a preferred form of the model, the segments display a middlepiece--which extends in wedge-like form from the headpiece to thefootpiece--between their headpiece, which forms the commutator path, anda footpiece; this middle piece is clamped in between the sides of thecorresponding groove. Thanks to the wedge form of this middle part, theclamping force acting on the sides of the middle part has a radialcomponent, which presses the surfaces of the segments, which areintended for radial positioning, against the surfaces of the hub bodycorresponding to them.

The radial positioning of the segments can take place by pressing theshoulders against the surface area of the crosspieces turned againstthem when--as is the case in a preferred working model--the width of theheadpiece of the segments--as measured in the circumferential directionof the commutator--is larger than the corresponding width of the middlepart, on which a shoulder (which overlaps the directly adjoiningcrosspieces of the hub body bordering the grooves on the sides) isdisplayed on each side on the ends that are connected to the headpieceand on the segments on the transition from the middle part to theheadpiece.

Preferably, the two shoulders of these segments overlap less than halfof the end surface of the directly adjoining crosspieces turned towardthem. Between the headpieces of the two adjoining segments the necessaryinterval, in circumferential direction, therefore exists. In thisconnection, the gap between the headpieces of adjoining segments is,preferably, free of the material parts of the hub body.

In a preferred working model, the footpiece of each segment, which isconnected to the wider end of the middle part in a first section,displays a reduced width--when forming a shoulder in the area of bothsides--and a larger width with respect to the first section in a secondsection that is connected to the first section--when forming a shoulderin the area of both sides. In this case the footpiece has across-sectional profile similar to a T.

Preferably, the middle part of the segments rests--all over thesurface--against the sides of the groove that takes them up. Instead ofa positioning of the shoulders of the segments, which exist at thetransition from the middle part to the headpiece, on the end surfaces ofthe crosspieces, one can also provide for a positioning of the endsurface of the footpiece, which is turned away from the headpiece, underpressure, at the base of the groove that takes up the segment for thepurpose of the radial positioning. The aforementioned positioning isespecially advantageous in the area of the lagging end of the segmentsand the positioning of the shoulders on the end surfaces of thecrosspieces in the area of the leading end.

In the application of the theory according to the invention, the size ofthe commutator and the relation between the spacing and the size of thecommutator are not important. In the case of plug-in commutators with asmall diameter and large spacing intervals, it can, however, be the casethat in maintaining the necessary distance between the individualsegments, the sides of the segments that serve as bearing surfaces aredesigned too short. To meet the demands made on performance it istherefore of advantage that the segments meant for anchoring have atleast two pair of bearing surfaces. Preferably, the angles between thepairs are different for each pair. In this way, one can be sure that allbearing surfaces rest against the crosspieces in spite of processtolerances.

During the production of customary commutators the segments are firstplaced in a basket, which specifies the positioning when the segmentsare inserted into the grooves. This basket is then put in an injectionmolding die or a compression molding die and is pressed or injected. Theplastic basket can only be used once. On the other hand, the basket isnot used in a process according to the invention in which the clampingforce is determined alone by the overdimension in the area of the endsections of the segments and/or the area of the material parts of thehub body that facilitate the positioning of the segments. The exactpositioning takes place through the areas that are not provided with anoverdimension. The clamping power, which builds up at the end of theinsertion procedure, no longer influences the positioning. With theelimination of the basket, both material savings and a shortening of themanufacturing process are linked to the steps of equipping and removingthe basket. By eliminating the basket it is also possible to bend thehooks, which serve to connect the segments electrically, in a toolduring the production of the segments. The bending process is left outof the work cycle.

It is more advantageous to choose the pressure and, if applicable, thetemperature during the insertion of the segments so that instead ofhaving, to a large extent, an insoluble molding bond between the hubbody and the segments, the hub body and the segments can be separatedfrom one another again. A plug-in commutator manufactured according tosuch a process is thus recyclable.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following the invention is illustrated by using two workingmodels that are represented in detail in the drawings.

FIG. 1 shows a front view of the first working model;

FIG. 2 shows a cut according to line II--II of FIG. 1;

FIG. 3 shows an enlarged cut-out from FIG. 2;

FIG. 4 shows a front view of one of the segments;

FIG. 5 shows an enlarged and incompletely represented cross section ofthe first working model in the area of the leading section of thesegments;

FIG. 6 shows a cross section of the first working example in the area ofthe lagging end section of the segments corresponding to FIG. 5:

FIG. 7 shows an enlarged and incompletely represented cross section ofthe second working model in the area of the lagging end section of thesegment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

A plug-in commutator displays a hub body (1), which consists of anelectrical isolation material and which is provided with open grooves(2) over its circumference that are evenly distributed and positioned,of like design, and run in axial direction as well as radially outward.As FIG. 2 shows, the grooves (2) begin at one end of the hub body (1),but end at a distance from the other end, whereby the end of all thegrooves (2) lies on a radial plane. The hub body (1) in the workingexample consists of a molding material on a phenol basis. Otherisolating materials, such as thermoplast or ceramic, can, however, beconsidered. In addition, the material can have fiber reinforcement.After production, the hub body (1) can be malleablized at a temperaturethat is above the working temperature.

In each of the grooves (2) a segment (4) is set up. The segments (4),which are of like design, consist of a material that conductselectricity well and is customary for commutator segments. As, forexample, FIG. 4 shows, the segments (4) display a headpiece (5), whosecylindrically bent end surface (5') forms a part of the commutator path.The segments (4) are designed so they are symmetrical to theirlongitudinal middle plane (6). On the headpiece (5), a middle part (8)is connected by forming a shoulder (7) in each case; the width of themiddle part--measured in circumferential direction--on the end passingthrough a rounded out section in the shoulders (7) is smaller than thewidth of the headpiece (5) by the width of the shoulders (7). Theshoulders form an open obtuse angle that opens toward the end surface(5'). The middle part (8) extends like a wedge from the headpiece (5) toa footpiece designated, as a whole, as 9. Both of its flat sides (8')form an angle of 20° in the working example. The footpiece (9) has afirst section (11) that is connected to the middle part (8) via ashoulder (10); the width of the first section in the area of theshoulders (10) is smaller than the width of the middle part (8) by thewidth of the shoulder. The width of the first section (11) growssteadily smaller toward the second section (12), which is connected toit. Connected in each case via a shoulder (13) is the second section(12), whose width grows steadily smaller toward its end surface (9').The footpiece (9) therefore has a cross-sectional profile shaped like aT.

As, in particular, FIG. 5 shows, when the segments (4) are inserted intothe grooves (2), both shoulders (7) overlap the crosspieces (14) of thehub body (1), which border the grooves on the sides, by less than halfof the end surface (15), which is turned toward the headpiece (5). Forthis reason a slot (16), into which no material parts of the hub body(1) project in the working example, exists between the two adjoiningsegments (4). The side surfaces of the headpiece (5), which border onthe slot (16), run parallel to each other.

As FIG. 5 further shows, the two sides (8') of the middle part (8) ofeach segment (4) rest--all over the surface--against the crosspieces(14). The part of each groove (2) that takes up the footpiece (9) has across-sectional form that is geometrically similar to the footpiece (9),but the measurements of the groove (2) in this part are a little largerthan the measurements of the footpiece (9). As a result, a small gap(17) exists between the footpiece (9) and the bordering side surfaces ofthe part of the grooves (2) that take up the footpiece (9).

As FIG. 3 shows, the crosspieces (14) in zone (18), in which the leadingend section of the segments (4) comes to a halt in a completely insertedstate--when the segments (4) are inserted in the grooves (2)--have anoverdimension on the end surfaces (15) of the crosspieces (14) in radialdirection; the overdimension (as FIG. 5, which represents a cut throughzone 18, shows) leads to the fact that the shoulders (7) rest--all overthe surface--against the end surfaces (15), with pressure, as a resultof which the clamping force, which is exerted on the sides (8') of themiddle part (8), is increased. The clamping power just mentioned has acomponent, which is set against the footpiece (9). The gap (17) extendsin zone (18) between the end surface (9') of the footpiece (9) and thebase of the groove (2). The axial length of the zone (18) with theoverdimension (x) amounts to about 15% of the axial length of thegrooves (2) in the working example. Via a ramp (19), the transitiontakes place from the zone (18) to the remaining part of the crosspieces(14), in which the end surfaces (15) of the crosspieces (14) have anegative overdimension, i.e., an underdimension (y). Wherever anunderdimension (y) exists, as FIG. 6 shows, a gap (20) exists betweenthe end surfaces (15) of the crosspieces (14) and the shoulders (7).

In the area of the end section that lags during the insertion of thesegments (4) into the grooves (2), the segments (4) have a zone (21)with an overdimension (z) in radial direction of the end surface (9') oftheir footpiece (9). This overdimension (z) has as a consequence--asFIG. 6, which represents the cut through the zone (21), shows--that theend surface (9') rests against the base of the corresponding groove (2),with pressure, and the clamping force rises, which the crosspieces (14)exert on the sides (8') of the middle part (8). As a consequence, anarrow slot (20) exists in the area of zone (21) between the shoulders(7) and the end surfaces (15) of the crosspieces (14).

The overdimensions (x and z) are chosen so that the clamping forcesexerted on the segments (4) do not fall below the value necessary toguarantee the positioning and determination of the segments (4) in thehub body (1).

But the force necessary for the simultaneous insertion of all thesegments (4) into the grooves (2) from the beginning of the insertionprocedure to the time zone (18) is reached by the leading end of thesegments (4) is, however, very small because in this case only theclamping force--at first very small--which the crosspieces (14) exert onthe middle part (8), must be overcome. Only when the leading end sectionof the segments (4) is inserted into the zone (18) does the necessaryinsertion force rise sharply and reach its maximum value when the endsurface (9') of the footpiece (9) enters the zone (21) in position atthe base of the corresponding groove (2), whereby this entrance is madeeasier through a ramp, which acts as a transition to the zone (21). Whenthe segments (4) are completely inserted into the grooves (2), theleading end rests, as FIG. 3 shows, against a surface (23), which liesat a distance from the adjoining conical forepart (24) of the hub body(1) in the working example, and borders on the groove (2) in axialdirection. All surfaces (23) lie on a common radial plane.

Hooks (25) in the working example, which are formed on the segments (4)and which facilitate the connection of the segments (4) to theconductors of a rotor coil, lie on the outer surface area of the endsection of the hub body (1), which borders on the surfaces (23) and theconical forepart (24).

A further working example concerns a plug-in commutator, whose segments(104) display two pairs of bearing surfaces, but which otherwise concursin all the details of the first working example, which have not beendescribed here. The middle part (108) of each segment (104) has a pairof sides (108'), which are designed as bearing surfaces on thecrosspieces (114) of the hub body (101), as in the first workingexample. The pair of sides (108'), opened radial inwards, forms an anglea. The footpiece (109) of each segment (104)--which lies radiallyinwards, has a further pair of sides (113), which are also designed asbearing surfaces on the crosspieces (114). This additional pair of sides(113) forms an angle α and also opens radially inwards. The angle βissmaller than angle α. In the limiting case β can equal 0°, that is, thesides (113) run parallel to each other.

When inserting the segments (104) in the grooves (102) of the hub body(101), the segments (104) are pressed radially outwards through theoverdimension in the end section. In so doing, the sides (113) providedon the footpiece (109) come into position with the crosspieces (114).Through the small angle α, the crosspieces (114) counteract theinsertion of the segments (104) with just a small force. With furtherinsertions, the sides (113) are pressed into the hub body (101) untilthe sides (108') provided on the middle part (108) come into positionwith the crosspieces (114). With the correct choice of the angles α andβ and the other dimensioning of the segments (104) and the crosspieces(114), all the pairs of sides (108' and 113) therefore come intoposition on the crosspieces (114). In the case of compression-proof hubbodies (101) it is advantageous when the crosspieces (114) in the areaof the footpieces (109) have a somewhat larger opening angle inwards incomparison with β. In this way only a part of the sides (113) comes intoposition--which reduces the counteracting force.

In the case of a process according to the invention, the hooks (25) arebent after the production of the segments (4, 104), which are still inthe tool. The segments (4, 104) are then pushed--i.e.,inserted--directly into the hub bodies (1, 101). The parameters forinsertion, especially the pressure and, if applicable, the temperature,are chosen in such a way that no insoluble molding bond arises.Alternatively, the boring of the hub body (1, 101) can be worked onafter the insertion of the segments (4, 104). Although certain presentlypreferred embodiments of the present invention have been specificallydescribed herein, it will be apparent to those skilled in the art towhich the invention pertains that variations and modifications of thevarious embodiments shown and described herein may be made withoutdeparting from the spirit and scope of the invention. Accordingly, it isintended that the invention be limited only to the extent required bythe appended claims and the applicable rules of law.

I claim:
 1. A plug-in commutator apparatus having a commutator surface,said apparatus comprising:a hub body made of an electrical isolatingmaterial, said hub body having radially and axially extendingcrosspieces and grooves provided between said crosspieces, wherein saidgrooves are evenly distributed and positioned along a periphery of saidhub body with outer surfaces of said crosspieces and openings to saidgrooves forming said periphery of said hub body; a plurality of segmentsinsertable in said grooves, each segment having a headpiece that formsat least a part of said commutator surface; and means for securing saidsegments in said grooves, said securing means selected from the groupconsisting of overdimensions located along surfaces at axial endsections of said crosspieces defining said grooves, overdimensionslocated along axial end sections of said segments, and overdimensionslocated along surfaces at said axial end sections of said crosspiecesdefining said grooves and said axial end sections of said segments,wherein said overdimensions cause said walls of said crosspiecesdefining said grooves to hold said segments when said segments are fullyinserted in said grooves.
 2. Apparatus according to claim 1, whereineach groove has a front section and a back section, wherein each segmenthas a leading end section and a trailing end section, wherein saidleading end sections of said segments are located in said back sectionsof said grooves when said segments are fully inserted in said grooves,wherein said trailing end sections of said segments are located in saidfront sections of said grooves when said segments are fully inserted insaid grooves, and wherein said securing means comprises overdimensionslocated along surfaces of said crosspieces forming said back sections ofsaid grooves and overdimensions located along trailing end sections ofsaid segments.
 3. Apparatus according to claim 2, wherein each of saidcrosspiece overdimensions has a first axial length, wherein each of saidsegment overdimensions has a second axial length, and wherein said firstaxial length is greater than said second axial length.
 4. Apparatusaccording to claim 1, wherein each of said segments further comprises aheadpiece, a footpiece, and a middle part having a first end connectedto said headpiece and a second end connected to said footpiece, saidmiddle part having bearing surfaces frictionally engaged by surfaces ofsaid crosspieces defining said groove.
 5. Apparatus according to claim4, wherein each of said segments is generally symmetrical to a centralaxis thereof.
 6. Apparatus according to claim 5, wherein said headpiecehas a width that is larger than a corresponding width of said middlepart, and wherein sloped shoulders connect said headpiece to said firstend of said middle part.
 7. Apparatus according to claim 6, wherein saidshoulders of each of said segments overlap at least a portion of saidouter surfaces of said crosspieces.
 8. Apparatus according to claim 7,wherein said shoulders overlap only a portion of said outer surfaces ofsaid crosspieces, and wherein gaps are formed between side surfaces ofadjacent headpieces.
 9. Apparatus according to claim 8, wherein nomaterial parts of said hub body project into said gaps.
 10. Apparatusaccording to claim 5, wherein said footpiece has a first sectionconnected to said second end of said middle part and a second sectionconnected to said first section, wherein said first section has a widththat is smaller than a width of said middle part, and wherein saidsecond section has a bottom base and a width that is larger than saidwidth of said first section.
 11. Apparatus according to claim 10,wherein said width of said first section grows steadily smaller fromsaid second end of said middle part to said second section of saidfootpiece, and wherein said width of said width of said second sectiongrows steadily smaller from said first section to said base. 12.Apparatus according to claim 5, wherein said middle part is engaged bysaid surfaces of said crosspieces forming said grooves at all stages ofinsertion.
 13. Apparatus according to claim 4, wherein said securingmeans comprises at least said overdimensions located along said surfacesat said axial end sections of said crosspieces defining said grooves,wherein each segment further comprises sloped shoulders connecting saidheadpiece to said first end of said middle part, and wherein saidshoulders press against said outer surfaces of said crosspieces atregions where said overdimensions are located.
 14. Apparatus accordingto claim 4, wherein said securing means comprises at least saidoverdimensions located along axial end sections of said segments,wherein each of sed segments has an inner base surface, and wherein saidinner base surfaces of said segments press against a bottom, innersurface of said groove at regions where said overdimensions are located.15. Apparatus according to claim 4, wherein said securing meanscomprises at least said overdimensions located along said surfaces atsaid axial end sections of said crosspieces defining said grooves, andwherein said surfaces of said crosspieces defining said groove furthercomprise ramped sections extending up to said overdimensions. 16.Apparatus according to claim 1, further comprising hooks formed on saidsegments.
 17. Apparatus according to claim 1, wherein each of saidsegments further comprises a headpiece, a footpiece, and a middle parthaving a first end connected to said headpiece and a second endconnected to said footpiece, and wherein said middle part and saidfootpiece have bearing surfaces that frictionally engage surfaces ofsaid crosspieces defining said groove.
 18. Apparatus according to claim17, wherein said bearing surfaces of said footpiece are continuous andslope inward and downward from said middle part at a first angle, saidbearing surfaces of said middle part are continuous and slope inward anddownward from said headpiece at a second angle, and wherein said firstangle is different than said second angle.
 19. A process formanufacturing a plug-in commutator comprising:providing a hub body madeof an electrical isolating material, said hub body having radially andaxially extending crosspieces and grooves provided between saidcrosspieces, wherein said grooves are evenly distributed and positionedalong a periphery of said hub body with outer surfaces of saidcrosspieces and openings to said grooves forming said periphery of saidhub body; a plurality of segments insertable in said grooves, eachsegment having a headpiece that forms at least a part of said commutatorsurface; and means for securing said segments in said grooves, saidsecuring means selected from the group consisting of overdimensionslocated along surfaces at axial end sections of said crosspiecesdefining said grooves, overdimensions located along axial end sectionsof said segments, and overdimensions located along surfaces at saidaxial end sections of said crosspieces defining said grooves and saidaxial end sections of said segments, wherein said overdimensions causesaid walls of said crosspieces defining said grooves to hold saidsegments when said segments are fully inserted in said grooves;inserting simultaneously all of said segments axially into said groovesof said hub body, wherein said inserting step further comprisesovercoming an insertion resisting force resulting from saidoverdimensions and fully inserting said segments in said grooves tosecure said segments against displacement relative to said hub body. 20.Process according to claim 19, further comprising providing hooks onsaid segments and electrically connecting said hooks following saidinserting step, said electrically connecting step further comprisingbending ends of said hooks.
 21. Process according to claim 19, whereinsaid segments are inserted in said grooves of said hub body undersufficient pressure and temperature such that said hub body and saidsegments can be separated from each other.